1. Field of the Invention
The present invention relates to an occupant detection system for detecting whether an occupant is present or absent in a vehicle, which is used for a system such as an air bag system for protecting an occupant at the time of a vehicle collision. In particular, the present invention relates to an occupant detection system mounted to a vehicle such as an automobile, which provides information as to whether an occupant is present or absent in a vehicle, the information being utilized for controlling: an air bag system for protecting an occupant at the time of a vehicle collision; an air conditioning system for controlling temperature inside a vehicle; an alarm system for warning an occupant of a critical condition such as his/her dozing; and the like.
2. Description of the Related Art
An air bag is used for protecting an occupant by immediately expanding between a steering wheel or a dashboard and the occupant at the time of a vehicle collision. However, there is a case where a driver is seated in a position close to the steering wheel because the driver is short or a case where a child stands in front of a front passenger seat. In such cases, a distance between the steering wheel or the dashboard and the occupant is extremely short. Thus, it is known that the expansion of the air bag causes damage to the occupant.
Also, in the case where the occupant in the front passenger seat is a child at the age of six or below, even when being seated in a normal position, it is presumed that it is safer not to expand the air bag. Therefore, in the United States, legislation enforcing obligatory installation of the occupant detection system in an occupant protection system using an air bag is the current tendency. As the occupant detection system that can be used for the occupant protection system, for example, a system described in Japanese Patent Laid-open No. 08-169289 is known.
A conventional occupant detection system is described with reference to the accompanying drawing. FIG. 4 is a diagram showing the structure of the conventional occupant detection system described in Japanese Patent Laid-open No. 08-169289.
In FIG. 4, reference numeral 10 denotes a vehicle such as an automobile; 11, a seat such as a driver seat or a front passenger seat which is provided in the vehicle 10; 12, an occupant seated in the seat 11; 13, a steering wheel; 14, an air bag provided inside the steering wheel 13 or in the dashboard at the front passenger seat 11; and 15, a distance sensor which is provided on a front ceiling of the vehicle 10 and faces in the direction of the seat 11. Symbol 16a denotes a seat position sensor for detecting a position along the front and rear direction of the seat 11, and symbol 16b denotes a seat position sensor provided in the seat back cushion of the seat 11 for detecting a reclining angle thereof.
Next, the operation of the occupant detection system of the conventional system will be described with reference to the drawing.
In the case where the seat 11 is vacant, the distance sensor 15 detects the position of the seat 11, and in the case where the occupant 12 is seated in the seat 11, the distance sensor 15 detects the position of a front surface of the occupant 12. When the detected position is too close to the air bag 14, expansion of the air bag 14 is judged to be more dangerous. Thus, even in the case of a frontal collision of the vehicle 10, the air bag 14 is restrained from expanding.
Also, in the case where the position obtained by the distance sensor 15 is identical to the position obtained from outputs of the seat position sensors 16a and 16b, it is judged that the occupant 12 is absent. In the case where the two positions are different, it is judged that the occupant 12 is present.
In the case of the frontal collision of the vehicle 10, it is necessary that, if the occupant 12 is present, the air bag 14 be expanded to thereby protect the occupant 12. However, it is uneconomical to expand the air bag 14 even in the case of the absence of the occupant 12. Therefore, in the case where the above-described judgment results in the absence of the occupant 12, the air bag 14 is restrained from expanding. As a result, the wasteful repair cost can be saved.
In the conventional occupant detection system described above, there is a problem in that in order to judge whether the occupant 12 is present or absent, besides the distance sensor 15 provided to the ceiling, it is necessary to provide the seat position sensors 16a and 16b in the seat 11 and long wirings for integrating the outputs of the seat position sensors 16a and 16b installed apart from each other.
Further, there is another problem in that the wirings are long, thereby causing inconvenience of mounting the system to the vehicle 10, which results in poor mounting property.